请教一道题目

Q22:

Four extra-large sandwiches of exactly the same size were ordered for m students, where m > 4.  Three of the sandwiches were evenly divided among the students.  Since 4 students did not want any of the fourth sandwich, it was evenly divided among the remaining students.  If Carol ate one piece from each of the four sandwiches, the amount of sandwich that she ate would be what fraction of a whole extra-large sandwich?

A： m+4/m(m-4)

B: 2m-4/m(m-4)

C: 4m-4/m(m-4)

D: 4m-8/m(m-4)

E: 4m-12/m(m-4)